Motor-control system.



PATENTED SEPT. 10, 1907.

W. H. POWELL.

MOTOR CONTROL SYSTEM.

APPLICATION FILED JULY 21.1mm.

INVENTOR WITNESSES William H.Powll AT TQRNE Y UNITED STATES PATENT OFFICE.

WILLIAM H. POWELL, OF NORWO'OD, OHIO, ASSIGNOR T ALLIS-CHALMERS COMPANY, A CORPORATION OF NEW JERSEY,-AND THE BULLOCK ELECTRIC MANUFACTURING COM- PANY, A CORPORATION OF OHIO.

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Specification of Letters Patent.

Patented Sept. 10, 1907.

- Application filed July 27, 1906- Ssrial No. 328,047.

To all whom it may concern:

Be it known that 1, WILLIAM H. POWELL, a citizen of the United States, residing at Norwood, in the county of Hamilton and State of Ohio, have invented 8 certain new and useful Improvements in Motor-Control Systems, of which the following is a full,- clear, and exact specification.

My invention relates to motor control systems and particularly to control systems for mill and hoisting l0 motors. V

In rolling mills and in hoisting machineryit is necessary that the ,moving parts be quickly and often reversed. Heretoiore, these have been driven mostlyby steam engines. It has been proposed, however, to

have electric motors for doing this worlcland to have a special generator, on whose shaft is a flywheel, for each motor, the regulating and reversing of the motor being accomplished solely by varying and reversing the field of the generator. This arrangement is very unsatisfactory because it necessitates generators and motors of much greater capacity than required by the load on the motor, for on account of the system of regulation employed, the maximum voltage is used with a current much below the maximum and the maximum current I with a voltage much less than the maximum. Moreover, the maximum current flows in the generator armature when the generator field is very weak, thus further disadvantage is that-the time required for the 80 reversal is too great, especially in rolling mills, where a reversal of direction must be made every few sec-' onds.

It is the object of my invention to overcome these disadvantages, and to provide a motor control system of great adaptability and with a wide range of speedcontrol. With my invention the size of the generators and motors may be very greatly reduced, because the maximum current ,is demanded at the same time or nearly the same time that the voltage is the greatest. The commutation is also facilitated because the generator has a comparatively strong field when the greatest current is demanded. Moreover, the time required for the reversal is greatly decreased because of the diminished time constant of the generator fieldsimultaneously strengthening its field and diminishing to zero the electromotive force impressed on its armature, and then simultaneously weakening its field and increasing in the reverse direction the electromotive force impressed on its armature. v a

In a more specific aspect, my invention comprises the method of operating an electric motor at a variable speed and load, which consistsin supplying mechanical energy, converting it into electrical energy, supplying the electrical energy to the motor, simultaneously and inversely varying the electromotive force of said electrical energy and the field strength of said motor, storing any excess of the mechanical energy when the power supplied exceeds the power demanded by the load, and supplying said stored energy to the motor as electrical energy when the power demanded by the load exceeds the power supplied.

From another point of view, my invention consists of a motor control system comprising a motor, a source of current for supplying the motor armature, a second source of current for supplying the motor field coil, and means for simultaneously and inversely varying the electromotive force of said first source of current and the field strength of the motor. I

In still another aspect my invention consists of a system of motor control comprising a motor, means for firstsimultaneously increasing the strength of its field manrmmismfig' measure electromotive force impressed on its armature, and for then simultaneously weakening its field and increasing in the reverse direction'theelectromotive force impressed on its armature.

.' In stilla more specific aspect my invention consists of a system of motor control, comprising a source of current, a motor supplied thereby, a flywheel mechanically connected to said motor, a generator driven by said motor, a second motor supplied by said generator,

Other features of my invention will appear from the {3i following description and accompanying drawings and will be particularly pointed out in the claims.

The single figure of the drawings shows diagrammat- 1 ically one embodiment of my invention.

motors could be usedinstead. this motor is a starting resistance 1 adjustable by means of a short-circuiting bar 2, and a regulating resistance 3 arranged tobe cut in and out by a solenoid BWltChfi which in turn is responsive to the current strength in the primary circuit of the motor, as through a series traniormer 5. Other means for varying the speed of motor A may be used if desired. A generator armature B is driven by the motor A, being prcferably'directly connected thereto, and on the common shaft of the motor A and generator B is a heavy fly-wheel C. The generator B supplies current to the armature D of the working motor. The motor D may be used to drive any desired machinery. 7

The field windings b of the generator, and (l of the working motor are supplied from any direct current source through a switch 6. These two field coils are controlled by a single controller H, which is arranged to simultaneously and inversely vary the resistances in circuit respectively with,these two field coils and to reverse the current in the coil b. The arm or handle h. of this controller is divided into several electrically distinct parts. There are two sets of variable resistances, one set of which, resistances 14 and 15, are for the field circuit of the generator, and the other set, 16 and.17,

for the field circuit of the working motor. With.sepa-- rate resistances for the generator and motor field circuits, it is possible to make the motor and generator substantial duplicates ofeach other,;which, because of the different variations tobe produced in: the two fields, is generally impossible if 'the sameiresistance isused for both field circuits. For this reason it is deemed' best have separate resistances for .the 'two field circuits, although in some instances a single resistance may suffice If desired, instead of having the resistances 14 and 15 separate, the contacts of one may be connected to the corresponding contacts of the other,

one of these resistances being omitted. The samev cross connection may be applied to the contacts of re- 7 sistances 16 and 17.

The controller is arranged so that when its arm h is moved on one side of the vertical'the resistances 14 and 17 are simultaneously and inversely varied to control the speed of the motor D in one direction, and when moved on the other side of the'vertical the resistances l5 and 16 are simultaneously and inversely varied to control the motor. D in the other direction, the direc-' tion of current through the coil b being reversed as the arm h passes through its vertical position. Between the segments 7 and 8 of the controller is arranged a' re sistance 9 to take up the field discharge when the circuit through the coil 1) is broken. The resistance 9 is aided in this by a high resistance 11 permanentlyconnected across the coil A non-inductive resistance 13 is connected in series 'with the field coil 1). This resistance has an ohmic value several times as great as that of the field coil with whichrit is in series. Thepurpose of this resistance is to diminish the time constant of the field magnet b, for the time constant of a circuit is a function of its inductance divided by, its resistance. Therefore by increasing the resistance of the field circuit without increasing its inductance, the current strength being kept the same, the time constant of the field magnet is reduced. By this means quick reversals of the motor D may be more readily obtained. If desired, a similar resistance 13 maybe placed in theworking motor field circuit in order to reduce its time constant, although the current in this circuit'is never reversed, but only varied in strength.

Particular attention is called to the relative arrangement of the contacts 14 and 17, and also of the contacts 15 and 16. These are so placed that when the arm h is moved to cut out resistance 14, at the same time that the arm h engages one of the contacts of resistance 14 to cut out a section of said resistance, italso leaves'the corresponding contact of resistance 17 to cut in a section thereof. The same applies when the arm is moved. to cut in resistance 14, for simultaneously with the cutting in of a section of resistance'lfi, a section of resistance 17 is cut out. .When the arm h is moved on the other side of the vertical the same simultaneous and inverse variation of the resistances 15 and 16 takes place.

The operation of the system is as follower-The primary circuit of motor A is closed and the motor started by moving the bar 2 to cut out the starting resistance 1.

The switch 4 is held open by its'solenoid at this time because of the heavy current requiredfor starting the motor. If'desired, other means may be used to insure I the open condition of this switch during starting. Af-

ter the motor has gained sufiicient speed and the starting resistance has been 61a out, the solenoid switch is allowed to closeto cut out resistance 3 because of the I D the desired direction of rotation. As this arm moves,

say anti-clockwise, it first connects the field coil 6 to the direct current source through the whole resistance 14 and then gradually cuts said resistance out of circuit with coil b. Simultaneously withthe cutting out of resistance 14, resistance 17 is cutinto circuit. This simirltaneous and inverse variation of the resistances 14 and 17, simultaneously increasesthe electromotive force delivered by armature B to armature D and weakens the field (1, thus for two reasons causing the motor D to increasc'in speed. The speed which the motor D acquires depends upon the extent of movement of the arm h, the full speed being reached when the full resistance 14 has been cut out and the full resistance 17 cut in.

If the load is heavy the working motor requires more power for its starting than the motor'A canfurnish. The current rising in the primary of the transformer 5 by reason of this heavy load, the switch 4 is opened,

thus inserting resistance 3 into ther'otor circuit of motor A. This increases the slip of motor A and permits the motor to slow down, thus allowing the fly wheel C to give up some of the mechanical energy it has stored,

which energy helps the motor A to drive thegenerator B to supply'electrical energy at the rate demanded by the motor D to drive its load.

As the arm h is moved backward toward the vertical, the field d is strengthened and the field b simultane ously weakened. The lattercauses the electromotive force of armature B to decrease. Both the increasing of its field strength and the decreasing of the electromotive force impressed upon its armature slow down the motor D, causing it to act as a generator to supply cuted of this motor.

rent to the armature B, the latter now serving as a motor to help restore energy to the fly wheel C. There is a powerful braking effect upon theworking motor due to its acting as a generator. The diminished current in the primary of transformer 5 also causes the solenoid switch 4 to close, thereby increasing the speed of motor A so that the latter may also supply energy to the flywheel C. The flywheel thus stores up any excess of energy supplied when the rate of such supply exceeds the rate at which energy is demanded by the working motor, and gives up said stored energy whenever the rate of energy demanded is greater than the rate of energy supplied. Whenever arm h leaves the contacts of resistance 14 and slides over the segments 7 and 8, the resistance 9 is connected in circuit with the coil b to take the field discharge thereform, the resistances l1 and 13 assisting in this. When the arm h is moved in the other direction from the vertical the above cycle isrepeated save that the working motor D is caused to rotate in the other direction.

With my invention it ispossible to more quickly re verse motors, especially those of large capacity, than has ever been done, and to do this with less waste of energy. It is also possible to diminish the carrying capacity of the mains which supply the motor A because of the greater uniformity with which energy is demand- The capacity of machines B and D can also be greatlyreduced because the maximum current and maximum voltage are demanded by the working motor at nearly the same time. Another great ad vantage of my invention is that the maximum annature current is less, and flows when the generator has a stronger field magnetism, commutation being thus greatly assisted. There are many other advantages of my invention which it is not necessary to point out, as they will be obvious to one skilled in the art.

When I use the term inversely in this description and in the claims, I do not wish to limit myself to exact inverse proportion but intend the term to include any increase in one and decrease in the other of the two things specified.

I have described my invention in what I now consider to be its preferredform, but I aim to cover all those obvious modifications which readily occur to one skilled in the art.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The method of operating an electric motor at variable speed, which consists in supplying mechanical energy at a substantially uniform rate, transforming the mechanical energy into electrical energy, supplying the electrical energy to the motor, simultaneously and inversely varying the electromotive force of the electrical energy and the iield strength of the motor. storing any excess of the sup plied mechanical euerg' beyond that demanded by the motor at any time. and supplying said stored energy to the motor whenever required.

2. The method of operating an electric motor at variable speed, which consists in varying its field strength, simul taneously and inversely varying the elcctromotivc force impressed on its armature, storing as mechanical energy any excess of supplied energy when the load on the motor is light, and supplying suid stored energy to the motor as electrical energy whenever the load on the motor is heavy.

The method of operating an electric motor at variable speed. which consists in converting mechanical energy into electrical energy. supplying the electrical energy to the motor. simultaneously and inversely varying the electromotive force of the electrical energy and the field strength of the motor, storing any excess of the mechanical energy when its rule of supply exceeds the power demanded by the motor at any time. and supplying said stored energy to the motor as electrical energy whenever the power demanded by the rumor is uln've that normally supplied.

4. The method of regulating the speed of an electric molor, which consists in supplying mechanical energy at a substantially uniform rate. converting said mechanical energy into electrical energy ll :1 variable rate, supplying the electrical energy to the armature of the motor, energizing the ficld of the motor from a separate source, simultaneously and inversely varying the electromotive force of the electrical energy and the tield strength of the motor. storing any excess of mechanical energy when its rate of supply exceeds the rate at which the electrical energy is required, and supplying said stored energy to the motor as electrical energy whenever the electrical energy is demanded at a rate which exceeds the normal rate at which the mechanical energy is supplied.

The method of reversing an electric motor, which consists in first simultaneously strengthening its field and diminishing to zero the electromotive force impressed on its armature, and then simultaneously weakening its held and increasing in the reverse direction the electromotive tore-e impressed on its armature.

6. The method of regulating and reversing an electric motor, which consists in supplying its armature from one source of current, supplying its field from another source of current. simultaneously diminishing to zero thr- Pl\" l motive force of said first source of current and stl'cllt'tllenlug the motor field. and then simultaneously increasing in the reverse direction the electromotive force of said first source or current and weakening the motor field.

7. The method of operating an electric motor at a variable speed and load, consisting in simultaneously and inversely varying its field strength and the electromot-ive force impressed on its armature. storing as mechanical en ergy the excess of energy when the supplied power exceeds the power demanded by the load, and supplying said stored energy to the motor as electric-ill energy when the power demanded by the load exceeds the supplied power.

8. The method or operating an electric motor at a variable speed and load, which conslsts in supplying mechan ical energy, converting it into electrical energy, supplying; the electrical energy to the motor, simultaneously and inversely varying the elecfromotiv'e force 0! said electrical energy and the field strength of said motor, storing any excess oi the mechanical energy supplied when its rate of supply exceeds the rate at which energy is demanded by the load, and supplying said stored energy to the motor as el ctrical energy when energy is demanded by the load at a, rate which exceeds the rate at which the mechanical energy is supplied.

9. A system of motor control, comprising a dynamo-elect ric generator driven by a source of substantially constant power, a motor supplied by the generator, means for simuL taneously and inversely varying the electromotive force of the generator and the field strength of the motor. and

means for mechanically storing any excess of energy sup plied by the driving source and supplying said stored n ergy to the motor whenever required.

10. A system of motor control, comprising a motor. means for simultaneously and inversely varying its hold strength and the eleciromotivc force impressed on iis armature, and means for mechanically storing uny exccrts of supplied energy when the load on the motor is light and for supplying said stored energy to the motor as electrical energy when the motor load is heavy.

11. A system of motor control, comprising a dynamoelectric generator, :1 motor supplied thereby, means for simultaneously and inversely varying the electroniotive force of the generator and the field strength of the motor. means for storing any excess of the mechanical energy supplied to the generator when its rate of supply exceeds the power demanded by the motor at any time, and means for causing said stored energy to be supplied to the motor whenever the power demanded by the motor is above that normally supplied.

12. -A motor control system comprising a source of substantially constant mechanical powcr, a generator driven thereby. a variably loaded motor whose armature is supplied by the generator. a separate source of current which supplies the field of the motor, means for simultaneously and inversely varying the electromotive force of the generutor and the field strength-of the motor. means for storing any excess of mechanical energy supplied by the source when its rate of supply exceeds the intent which electrical energy is demanded by the load on the motor, and means for causing said stored energy to be supplied to the motor as electrical energy whenever the electrical energy isdemanded at a rate which exceeds the normal rateat which the mechanical energy is supplied. 7

' 13. A system of motor control, comprising a motor, and means for iirst simul'taneously increasing the strengthof its field and diminishing to zero the electromotive force:

impressed on its armature, and for then weakening-its field and increasing in the reverse direction the electromotive force impressed on its armature.

14. A motor control system comprising a motor, a source of current for supplying the motor armature, a second, source of current for supplying the motor field coilpand] means for simultaneously and inversely varying the electromotive force of said first source of current and the field and means for simultaneously and inversely varying the field strengths of the generator and'the motor. V 17. A system of motor, control, comprising an electric motor, asou'rce of currentsupplyingthe motor armmture, asecond source of currentsupplying the motor field coils} and means for first simultaneously diminishing to zero the electromotive force of said first source of current'andf strengthening the motor fieidf and then simultaneously increasing in the reverse direction the electromotive force; "of said first sourceof current and weakening the motori field. I

18. A motor control system comprising arnotor,means for simultaneously and inversely varying its field strength and, the electromotive' force impressed ou its armature, means for mechanically'storing any excess of energy when the suppliedpower exceeds the power demanded "by thev motor load,. and means for causing,saldpsmleilmneagyww behufiplidtd'the inotbr as electrical energy. when the power demanded by power. Q

19. A motor control system,"comprising-annexe of mechanical power, a dynamo --elec'tric -generator driven the motor loadiexceeds the applied thereby, armotor supplied by ,the generator, means for si multaneou'sly and inversely varying the ele ctromotiveforce of said generator and the fleld strength of said motor, means for storing'anycxcea's off mechanical'lenergy supplied by said source when its rate of supply exceeds the rate at which energy is demanded byf the motor-load, and' means for causing saidsto'red energy to be supplied to the motor as electrical energy when energy isfidemanded hy the motor load at a rate which .exceeds'the rate atwhich mechanical energy is supplied by the' source. i

20. In combination, a source. of power, a generator driven thereby, a motor supplied by the generator, means for simultaneously and inversely varying the field strengths of the generatorand themotor, a flywheel mechanically connectedto said. source'of power, and means for causing the flywheel to give upits energy when theload on the motor rises above the normal. 7 1

21. In combinatiomza source of power, a generator driven thereby, a motor suppliedg'by" the generator, means for simultaneously and inversely varying the resistances of the field circuits of the generator and the motor, ally wheel on the generator shaft, and means for allowing laid flywheel to give up its energy when the motor load risen above normal.

22. A system of motor control, comprising a motor, a generator supplyiug said motor. a flywheel on said generator shaft, and means for simultaneously and inversely varying the. field strengths of said generator and said motor.

23. A system of motor control, comprising a motor, a

generator supplying said motor, a flywheel on said generntor shaft, means for simultaneously and inversely varying the field strengths of said generator and said motor, and means for permitting the flywheel to give up its energy when the load on the moi'or is heavy. v

24. A system of motor control, comprising av motor, a generator supplylngsaid motor, a flywheel on the generutor shaft, means for permitting the flywheel to give up its j ener gy whenever the load on the motor exceeds a predetermineri value, and a controller tor-simultaneously and inversely varying the field strengths of the generator and the motor to va1'y tlie speed or the motor'and to cause energy to be restored to the flywheel while the motor is being retarded. I r

2-). A system of motor control, comprising a motor, a generator supplying said motor-,Ia flywheel on said gener'utorshaft', means for simultaneously and inversely varying the field strengths of said generator ,and said motor, and means forcausing the generator to run slower when the motor load is heavy than when the motor'load is light.

26. A system of motor control, comprising a motor, a generator supplying the armature ofsaid motor, a separate source of current supp lying the field coils of said generator and said motor, a'iiywheel on said generator shaft, and means-forsimdltaneously and inversely varying *the field strengths of said generator and said motor.

27. A system of motor control, c'omprisinga motor, a generator supplying the; armature of said motor, a fly- ;wh'eel on said generator shaft, means for simultaneously and inversely varying t hefieldstreng ths of' said generator and ,said motor, and means for allowing the flywheel to give upf'its energrwhen the load o'n the motor is 28. A system 'of motor'control, comprising a motor, a

. gen'e'rator supplying the armature thereof, a ,flywheel on -*the generator shaft, means for permitting the'flywheel to givev up its energy-whenever the load onthe motor exceeds a predetermined value, and a controller for .si

multaneously and inversely varying the field strengths of t e generator and the motor'to vary thespeed of the motor and to cause energy to be restored to the flywheel @while the motor is being retarded.

29. 'A system of motor control, comprising a motor a generator supplying the armature of said motor, a fly- ;n heelwon saidag wnator shatt mcana Jon simultaneously nd inverselyjvarying the fleld strengths of. said gener ator and said motor, and means for permitting the generator to run slower when'the motor is heavily loaded than it does wh'enthe motor is'lightly'loaded. 230. 'A' system of motor control, comprising an induction-motor, a generator driven thereby, a. flywheel on the shaft of saidi nduction motor, a working motor supplied yzlaid-generator and means for simultaneously and inerse ly varying the field strength of the working motor d the electromotive force of'the generator.

31: A system of motor control, comprising an induction -ton-fa"generator directly connected thereto, a flywheel oakth'e shaft oftthe, induction motor, a working motor supplied by the generator, andmeans for simultaneously and inversely ,yaryingfthe field strengths of the generator and I ,the working motor. V

32. A-system of motor control, comprisingan induction motor, a generator driven thereby, a flywheel on the shaft 'of 'the generator, aworking motor supplied by the generntorfmeans for simultaneously and inversely varying the fleldstrength" of theworking motor and the electromotive force of the generator, and means for decreasing ,the speed'of the-induction motor when a heavy load is placed on the working motor.

33. A system of motorcontrohcomprising a generator, a motor whoselarmature is supplied thereby, a separate Jsource ofcurrent supplying the field coils of the generator andthe motor, and means for simultaneously and invrsely varying the resistance! of said field circuits and for reversing said generator field circuit after its re- I sistance has been increased to the maximum.

34. A system of motor control, comprising u source of current, a motor supplied thereby, a flywheel mechanically connected to said motor, a generator driven by said motor, a second motor supplied by said generator, means for simultaneously and inversely varying the tield strengths of said second motor and said generator, and means for allowing said first motor to decrease in speed when the load on the second motor increases.

35. A system of motor control, comprising a generator, a motor supplied thereby, means for simultaneously and inversely varying the field strengths of said generator and said motor and tor reversing said generator field, and a resistance permanently in said generator field circuit.

36. A system of motor control, comprising a generator, a motor supplied thereby, means for simultaneously and inversely varying the field strengths of said generator and said motor and for reversing said generator field, and resistances permanently in the field circuits of the generator and the motor.

37. A system of motor control comprising a generator,

' a motor supplied thereby. resistances in the lield circuits of said generator and said motor, means for simultaneousiy and inversely varying said resistances and for reversing the current in the generator field circuit after the full resistance in said circuit has been cut in, and a high stance connected across the generator field terminals.

S. in combination, a separately excited generator, a separately excited motor the armature of which is supplied exclusively by said generator, and means for simultaneously and inversely varying the field strengths of said generator and said motor.

In testimony whereof I aiiix my signature, in the presence 0! two witnesses.

\VILLIAM H. POWELL.

Witnesses:

Gno. B. Scnnnr, Fmro J. KINSEY. 

